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Phosphonic Acid (Phosphorous Acid) is used in stabilizing mixtures for plastic materials.
Phosphonic Acid (Phosphorous Acid) is used for inhibiting high-temperature of corrosion-prone metal surfaces and to produce lubricants and lubricant additives.
Phosphonic Acid (Phosphorous Acid), H3PO3, is diprotic (readily ionizes two protons), not triprotic as might be suggested by this formula.
Phosphonic Acid (Phosphorous Acid) is as an intermediate in the preparation of other phosphorous compounds.
Because preparation and uses of “phosphorous acid” actually pertain more to the major tautomer, Phosphonic Acid (Phosphorous Acid), it is more often referred to as “phosphorous acid”.
Phosphonic Acid (Phosphorous Acid) has the chemical formula H3PO3, which is best expressed as HPO(OH)2 to show its diprotic character.
Phosphonic Acid (Phosphorous Acid) has been shown to be a stable tautomer.
Phosphonic Acid (Phosphorous Acid) is a phosphorus oxoacid.
Phosphonic Acid (Phosphorous Acid) is a conjugate acid of a dihydrogenphosphite.
Phosphonic Acid (Phosphorous Acid) is a tautomer of a phosphonic acid.
Phosphonic Acid (Phosphorous Acid) appears as a white or yellow crystalline solid (melting point 70.1 deg C) or a solution of the solid.
Density 1.651 g /cm3.
Contact may severely irritate skin, eyes, and mucous membranes.
Toxic by ingestion, inhalation and skin absorption.
Phosphonic Acid (Phosphorous Acid) Chemical Properties
Melting point: 73 °C
Boiling point: 200 °C
Density: 1.651 g/mL at 25 °C(lit.)
Vapor pressure: 0.001Pa at 20℃
Fp: 200°C
Storage temp.: 0-6°C
Solubility: DMSO (Slightly), Methanol (Slightly), Water (Sparingly)
Form: Crystals
pka: pK1 1.29; pK2 6.74(at 25℃)
Specific Gravity: 1.651
Color: White
PH: pKa1= 1.10, pKa2 = 6.33(25℃)
Water Solubility: SOLUBLE
Sensitive: Air Sensitive & Hygroscopic
Merck: 14,7346
Stability: Stable. Incompatible with strong bases. Hygroscopic.
CAS DataBase Reference: 13598-36-2(CAS DataBase Reference)
NIST Chemistry Reference: (HO)2HPO(13598-36-2)
EPA Substance Registry System: Phosphonic Acid (Phosphorous Acid) (13598-36-2)
Phosphonic Acid (Phosphorous Acid) is a white crystalline deliquescent solid that can be prepared by the action of water on phosphorus( III) oxide or phosphorus(III) chloride.
Phosphonic Acid (Phosphorous Acid) is a dibasic acid producing the anions H2PO3- and HPO3 2- in water.
The acid and its salts are slow reducing agents.
On warming, phosphonic acid decomposes to phosphine and phosphoric(V) acid.
Phosphorus acid is used to prepare phosphite salts.
Phosphonic Acid (Phosphorous Acid) is usually sold as a 20% aqueous solution.
Physical properties
White crystalline mass; deliquescent; garlic-like odor; density 1.651 g/cm3 at 21°C; melts at 73.6°C; decomposes at 200°C to phosphine and phosphoric acid; soluble in water, about 310 g/100mL; K1 5.1x10-2 and K2 1.8x10-7; soluble in alcohol.
Uses
Phosphonic Acid (Phosphorous Acid) is used to produce the fertilizer phosphate salt like potassium phosphite, ammonium phosphite and calcium phosphite.
Phosphonic Acid (Phosphorous Acid) is actively involved in the preparation of phosphites like aminotris(methylenephosphonic acid) (ATMP), 1-hydroxyethane 1,1-diphosphonic acid (HEDP) and 2-phosphonobutane-1,2,4-tricarboxylic Acid (PBTC), which find application in water treatment as a scale or corrosive inhibitor.
Phosphonic Acid (Phosphorous Acid) is also used in chemical reactions as a reducing agent.
Phosphonic Acid (Phosphorous Acid)'s salt, lead phosphite is used as PVC stabilizer.
Phosphonic Acid (Phosphorous Acid) is also used as a precursor in the preparation of phosphine and as an intermediate in the preparation of other phosphorus compounds.
Widely used as the raw materials to make phosphorous acid salt,used as the raw materials for making of plasticstabilizator in the plastic industry,used as reducer in chemical reaction,also used in the olefin industry, agricultural chemical industry and so on.
The most important use of Phosphonic Acid (Phosphorous Acid) is the production of basic lead phosphite, which is a stabilizer in PVC and related chlorinated polymers.
Phosphonic Acid (Phosphorous Acid) is used in the production of basic lead phosphonate PVC stabilizer, aminomethylene phosphonic acid and hydroxyethane diphosphonic acid.
Phosphonic Acid (Phosphorous Acid) is also used as a strong reducing agent and in the production of synthetic fibres, organophosphorus pesticides, and the highly efficient water treatment agent ATMP.
Ferrous materials, including steel, may be somewhat protected by promoting oxidation ("rust") and then converting the oxidation to a metalophosphate by using Phosphonic Acid (Phosphorous Acid) and further protected by surface coating.
Phosphonic Acid (Phosphorous Acid) may be used as one of the reaction components for the synthesis of the following:
α-aminomethylphosphonic acids via Mannich-Type Multicomponent Reaction
1-aminoalkanephosphonic acids via amidoalkylation followed by hydrolysis
N-protected α-aminophosphonic acids (phospho-isosteres of natural amino acids) via amidoalkylation reaction
Industrial uses
This collector was developed recently and was used primarily as specific collector for cassiterite from ores with complex gangue composition.
On the basis of the Phosphonic Acid (Phosphorous Acid), Albright and Wilson had developed a range of collectors mainly for flotation of oxidic minerals (i.e. cassiterite, ilmenite and pyrochlore).
Very little is known about the performance of these collectors.
Limited studies conducted with cassiterite and rutile ores showed that some of these collectors produce voluminous froth but were very selective.
Preparation
Phosphonic Acid (Phosphorous Acid) can be prepared by the reaction of phosphorus trichloride with water:
PCl3 + 3H2O → H3PO4 + 3HCl
The reaction is violent.
Addition of PCl3 should be extremely cautious and slow.
The addition can be carried out safely in the presence of concentrated HCl.
Alternatively, a stream of air containing PCl3 vapor is passed into icecold water and solid crystals of H3PO4 form.
Alternatively, Phosphonic Acid (Phosphorous Acid) can be prepared by adding phosphorus trichloride to anhydrous oxalic acid:
PCl3 + 3(COOH）2 → H3PO3 + 3CO + 3CO2 + 3HCl
In this reaction, all products except H3PO3 escape as gases leaving the liquid acid.
Dissolution of phosphorus sesquioxide in water also forms Phosphonic Acid (Phosphorous Acid).
When shaken with ice water, phosphorus acid is the only product.
P4O6 + 6H2O → 4H3PO3
However, in hot water part of the Phosphonic Acid (Phosphorous Acid) disproportionates to phosphoric acid and phosphorus or phosphine.
Preparation
On an industrial scale, the acid is prepared by hydrolysis of phosphorus trichloride with water or steam:
PCl3 + 3 H2O → HPO(OH)2 + 3 HCl
HPO(OH)2 could be produced by the hydrolysis of phosphorus trioxide:
P4O6 + 6 H2O → 4 HPO(OH)2
Reactions
Acid–base properties
Phosphorous acid has a pKa in the range 1.26–1.3.
HP(O)(OH)2 → HP(O)2(OH)− + H+ pKa = 1.3
Phosphonic Acid (Phosphorous Acid) is a diprotic acid, the hydrogenphosphite ion, HP(O)2(OH)− is a weak acid:
HP(O)2(OH)− → HPO2−3 + H+ pKa = 6.7
The conjugate base HP(O)2(OH)− is called hydrogen phosphite, and the second conjugate base, HPO2−3, is the phosphite ion.
The hydrogen atom bonded directly to the phosphorus atom is not readily ionizable.
Chemistry examinations often test students' appreciation of the fact that not all three hydrogen atoms are acidic under aqueous conditions, in contrast with H3PO4.
Redox properties
On heating at 200 °C, Phosphonic Acid (Phosphorous Acid) disproportionates to phosphoric acid and phosphine:
4 H3PO3 → 3 H3PO4 + PH3
This reaction is used for laboratory-scale preparations of PH3.
Phosphonic Acid (Phosphorous Acid) slowly oxidizes in air to phosphoric acid.
Both Phosphonic Acid (Phosphorous Acid) and its deprotonated forms are good reducing agents, although not necessarily quick to react.
They are oxidized to phosphoric acid or its salts.
Phosphonic Acid (Phosphorous Acid) reduces solutions of noble metal cations to the metals.
When Phosphonic Acid (Phosphorous Acid) is treated with a cold solution of mercuric chloride, a white precipitate of mercurous chloride forms:
H3PO3 + 2 HgCl2 + H2O → Hg2Cl2 + H3PO4 + 2 HCl
Mercurous chloride is reduced further by phosphorous acid to mercury on heating or on standing:
H3PO3 + Hg2Cl2 + H2O → 2 Hg + H3PO4 + 2 HCl
Reactivity Profile
Phosphonic Acid (Phosphorous Acid) decomposes when heated to form phosphine, a gas that usually ignites spontaneously in air.
Absorbs oxygen from the air to form phosphoric acid.
Forms yellow deposits in aqueous solution that are spontaneously flammable upon drying.
Reacts exothermically with chemical bases (for example: amines and inorganic hydroxides) to form salts.
These reactions can generate dangerously large amounts of heat in small spaces.
Dissolution in water or dilution of a concentrated solution with additional water may generate significant heat.
Reacts in the presence of moisture with active metals, including such structural metals as aluminum and iron, to release hydrogen, a flammable gas.
Can initiate the polymerization of certain alkenes.
Reacts with cyanide compounds to release gaseous hydrogen cyanide.
May generate flammable and/or toxic gases in contact with dithiocarbamates, isocyanates, mercaptans, nitrides, nitriles, sulfides, and strong reducing agents.
Additional gas-generating reactions occur with sulfites, nitrites, thiosulfates (to give H2S and SO3), dithionites (to give SO2), and carbonates (to give CO2).
Health Hazard
TOXIC; inhalation, ingestion or skin contact with material may cause severe injury or death.
Contact with molten substance may cause severe burns to skin and eyes.
Avoid any skin contact.
Effects of contact or inhalation may be delayed.
Fire may produce irritating, corrosive and/or toxic gases.
Runoff from fire control or dilution water may be corrosive and/or toxic and cause pollution.
